Variables in the real world are measured using analogue signals which are waves i.e. like a sound wave. An analogue wave looks something like this:

So, in order for a computer to understand the readings from a sensor it needs an Anologue to Digital Converter (ADC) which converts the analogue signal picked up from sensor a digital signal for the microprocessor (computer) to understand the reading.. The process is illistrated below:

Types of Sensor

The examiners will expect you to name different types of sensors and describe where they could be used. It is important that you learn the names of the sensors if you are aiming for a high grade.

Sensor

Advantage

Disadvantage

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Pressure sensor

Used to input pressure readings to a microprcessor or computer. Found in alarm systems , automatic doors, weighing scales, automatic washing machines, robotics and production lines

Much more accurate than traditional weighing devices because able to detect very small changes in pressure

As with other sensors, data doesn't have to be read manually

Any object of a suitable weight can incorrectly activate it

An ADC is requires

Temperature sensor

Used to input temperature readings into a microprocessor or computer. Used in microprocessor controlled washing machines, computer controlled green houses and microprocessor controlled heating systems

Much more accurate than traditional thermometers and able to detect very small temperature changes

Data does not need to be read manually - the microprocessor does it automatically

An ADC is required to input the signal into a computer

Light sensor

Used to input light readings to a microprocessor or computer. Used in automated street lights (turn off lights in day and on lights at night).

Able to detect very small changes in light levels

Data does not have to be read manually

An ADC is required to input reading into a computer

Can be activated incorrectly with artificial light

Humidity/Moisture

Used in automatic greenhouses, environmental monitoring, factories where moisture levels are critical such as paint spraying

Able to detect very small changes in moisture

Date does not have to be read manually

An ADC is required to input the reading

pH

Used in automatic greenhouses, chemical processes and environmental monitoring

Able to detect very small changes

Does not have to be manually read

An ADC is required to input reading to a computer

Aiming Higher

Although these sensors are the main ones you need to be aware of, examiners will often test your scientific understand and expect to be aware of additional sensors. Sensors mentioned in previous exam papers also include:

Water level sensor- to measure the level of water

Oxygen sensor- to measure the level of oxygen in water for environmental monitoring